The semiconductor integrated circuit (IC) industry has experienced rapid growth. Modern integrated circuits are made up of literally millions of active devices such as transistors and capacitors. Technological advances in IC materials and design have produced generations of ICs where each generation has smaller and more complex circuits than the previous generation. These devices are initially isolated from each other, but are later interconnected together through multiple metal layers to form functional circuits. As the IC becomes increasingly more complex, the interconnect structure also becomes more complex, resulting in increasing number of metal layers.
Interconnect structures may include lateral interconnections, such as metal lines (wirings), and vertical interconnections, such as conductive vias and contacts. However, complex interconnects limit performance and the density of modern integrated circuits.